Stratigraphical and paleoenvironmental new constraints in Benevento basin deposits (Early Pliocene, Southern Apennines)

The wedge-top depozone sequences of the Pliocene Foreland Basin System are well exposed in the Southern Apennines.Detailed analysis of lithology and sedimentary facies of deposits cropping out near Benevento has contributed to defining a sedimentary succession, about 400 meters thick. The succession lies unconformably on a basement formed by the Flysch Rosso Formation (Lagonegro Unit), cropping out in the northern border of the study area, and by elastic deposits of the Castelvetere Formation and Altavilla Unit; all are scaled by Quaternary alluvial and volcanic deposits. The presence of unconformities at the top and bottom of the succession allows it to be represented as an Unconformity Bounded Stratigraphic Unit (UBSU, sensu SALVADOR, 1994). The succession was divided, on lithostratigraphic criteria, into five informal units, with gradational vertical and lateral passages between them and with reduced thickness of transitional sediments:- Valle del Sabato conglomerate member: clast-supported weakly cemented conglomerates, with abundant coarse-grained sandy matrix, often embricates.- S. Leucio sand member: yellow-grey well stratified sands, with frequent clay or fine-grained pebble lenses or intercalated horizons.- Tufara Valle clay member: fossil-rich, blue-grey, well stratified clays and silty clays, with parallel laminated sand and silt intercalations.- Upper sand member: massive, yellow-grey sands, irregularly organized in beds, in places with thin pelitic intercalations, with lithologic and sedimentary features similar of those of the lower sandy deposits.- Upper conglomerate member: clast-supported conglomerates, with abundant sandy matrix, poligenic and heterometric pebbles, well rounded and embricates.Biostratigraphical analysis on deposits of the Tufara Valle clay member showed the presence of Globorotalia puncticulata throughout the succession, allowing it to be referred to the upper Early Pliocene. These new biostratigraphical data allow the analyzed succession to be correlated with the "Unite della Baronia" (AMORE et alii, 1998) or with the "Sintema della Baronia" (CIARCIA et alii, 2003) cropping out in the Irpinia region. The analysis of detailed stratigraphic sections has made it possible to identify and interpret facies associations related to alluvial, coastal-marine and shelf-marine environments.The lateral and vertical variations allows reconstruction of the studied area's main tectono-stratigraphic and paleogeographic evolution-tracts. On the whole several evolutionary stages are recognized:I) After the Messinian-lower Early Pliocene tectonic phase a large part of the area was emerged, with a very narrow basin and the development of a sub-aerial drainage network, feeding the Monte Colonna, San Leucio and Petruro-Chianche's alluvial-fan-systems;II) In upper Early Pliocene a generalized marine ingression took place, causing a marine basin widening. The border migrated southward in the Ceppaloni-S. Lcucio area and the coarse-grained elastic supply was interrupted;III) After the marine ingression maximum flooding, at least one syn-sedimentary tectonic event took place in the studied area, with a consequent uplift of a NW-SE oriented belt in the central-eastern sector of the area. This event caused a variation in drainage directions and a westward depozone's migration. During this phase the rapid erosion of emerged areas brought to an increase in the sedimentation rates, with the development of regressive sequences. Consequently the shoreline migrated seaward and alluvial systems widened.